High pressure separation of dimethyl ether from an olefin stream

Abstract

Disclosed is a method of removing dimethyl ether from an ethylene and/or propylene containing stream. Dimethyl ether is removed at a high pressure, preferably in a distillation column. The high pressure separation has the benefit of providing a relatively low bottoms temperature separation, while allowing for recovery of a highly concentrated ethylene and/or propylene stream.

1. A method of separating dimethyl ether from an olefin stream, comprising:
 contacting oxygenate with a molecular sieve catalyst to form an olefin stream, wherein the olefin stream contains ethylene, ethane, propylene, propane, and dimethyl ether; and 
 separating the olefin stream into a first fraction and a second fraction at a pressure of at least 200 psig in a distillation column having trays, wherein the first fraction contains at least a majority of the ethylene and propylene present in the olefin stream, the second fraction contains at least a majority of the dimethyl ether present in the olefin stream, and the olefin stream being separated further contains water in an amount not greater than 5,000 wppm so that free water formation or gas hydration does not significantly impede the separation. 
 
     
     
       2. The method of  claim 1 , further comprising contacting the olefin stream formed from contacting the oxygenate with the molecular sieve catalyst with water absorbent prior to separating into the first and second fraction. 
     
     
       3. The method of  claim 2 , wherein the water absorbent is contacted with the olefan stream at a molar ratio of water absorbent to total olefin of 1:2 to 1:200. 
     
     
       4. The method of  claim 1 , wherein the pressure is from 200 to 290 psig. 
     
     
       5. The method of  claim 4 , wherein the pressure is from 250 to 290 psig. 
     
     
       6. The method of  claim 1 , wherein the first fraction contains at least a majority of the propane present in the olefin stream. 
     
     
       7. The method of  claim 1 , wherein the first fraction contains not greater than 100 wppm dimethyl ether. 
     
     
       8. The method of  claim 1 , wherein the second fraction contains at least a majority of the propane present in the olefin stream. 
     
     
       9. The method of  claim 1 , wherein water absorbent is added to the distillation column. 
     
     
       10. The method of  claim 1 , wherein the second fraction has an average temperature of not greater than 250° F. 
     
     
       11. The method of  claim 10 , wherein the second fraction has an avenge temperature of not greater than 240° F. 
     
     
       12. The method of  claim 11 , wherein the second fraction has an average temperature of not greater than 230° F. 
     
     
       13. The method of  claim 9 , wherein the water absorbent is added to the distillation column at a molar ratio of water absorbent to total olefin stream to be separated of from 4:1 to 1:5,000. 
     
     
       14. The method of  claim 1 , wherein the provided olefin stream further comprises CO 2 , and the first fraction further contains at least a majority of the CO 2  in the provided olefin stream. 
     
     
       15. The method of  claim 14 , further comprising acid gas treating the first fraction. 
     
     
       16. The method of  claim 1 , wherein the provided olefin stream further comprises C 4 + hydrocarbon components, and the second fraction further contains at least a majority of the C 4 + hydrocarbon components in the provided olefin stream. 
     
     
       17. The method of  claim 1 , further comprising separating the ethylene and propylene in the first fraction and polymerizing the ethylene. 
     
     
       18. The method of  claim 1 , further comprising separating the ethylene and propylene in the first fraction and polymerizing the propylene. 
     
     
       19. The method of  claim 1 , further comprising contacting the first fraction wit water, acid gas treating the water contacted first fraction, and drying the acid gas treated first fraction. 
     
     
       20. A method of separating dimethyl ether from an olefin stream, comprising:
 contacting oxygenate with a molecular sieve catalyst to form an olefin stream, wherein the olefin stream contains ethylene, ethane, propylene, propane, dimethyl ether and water; 
 removing water from the olefin stream so that the olefin stream contains less than 5,000 wppm water; and 
 separating the olefin steam containing less than 5,000 wppm water into a first fraction and a second fraction in a distillation column having trays at a pressure of at least 200 psig so that free water formation or gas hydration does not significantly impede the separation, wherein the first fraction contains at least a majority of the ethylene and propylene present in the olefin stream, and the second fraction contains at least a majority of the dimethyl ether present in the olefin stream. 
 
     
     
       21. The method of  claim 20 , wherein the water is removed from the olefin stream by contacting the olefin stream with water absorbent at a molar ratio of water absorbent to total olefin of 1:2 to 1:200. 
     
     
       22. The method of  claim 20 , wherein water absorbent is added to the distillation column. 
     
     
       23. The method of  claim 22 , wherein the water absorbent is added to the distillation column at a molar ratio of water absorbent to total olefin stream to be separated of from 4:1 to 1:5,000. 
     
     
       24. The method of  claim 23 , wherein the olefin stream is separated at a pressure of from 200 to 290 psig. 
     
     
       25. The method of  claim 20 , wherein the provided olefin stream further comprises CO 2  and the first fraction further contains at least a majority of the CO 2  in the provided olefin stream. 
     
     
       26. The method of  claim 25 , further comprising acid gas treating the first fraction. 
     
     
       27. The method of  claim 20 , wherein the provided olefin stream further comprises C 4 + hydrocarbon components, and the second fraction further contains at least a majority of the C 4 + hydrocarbon components in the provided olefin stream. 
     
     
       28. The method of  claim 20 , further comprising separating the ethylene and propylene in the first fraction and polymerizing the ethylene. 
     
     
       29. The method of  claim 20 , farther comprising separating the ethylene and propylene in the first fraction and polymerizing the propylene. 
     
     
       30. The method of  claim 20 , further comprising contacting the first fraction with water, acid gas treating the water contacted first fraction, and drying the acid gas treated first fraction. 
     
     
       31. The method of  claim 2  or  21 , wherein the water absorbent is selected from the group consisting of alcohols, amines, amides, nitriles, heterocyclic nitrogen containing compounds, or a combination thereof. 
     
     
       32. The method of  claim 2  or  21 , wherein the olefin stream being separated contains not greater than 1,000 ppm water.